import falcon


def get_statistics_shards():
    """Enumerate the cores in Solr to determine if statistics have been sharded into
    yearly shards by DSpace's stats-util or not (for example: statistics-2018).

    Returns:
        str:A list of Solr statistics shards separated by commas.
    """
    from .config import SOLR_SERVER

    import re
    import requests

    # Initialize an empty list for statistics core years
    statistics_core_years = []

    # URL for Solr status to check active cores
    solr_query_params = {"action": "STATUS", "wt": "json"}
    solr_url = SOLR_SERVER + "/admin/cores"
    res = requests.get(solr_url, params=solr_query_params)

    if res.status_code == requests.codes.ok:
        data = res.json()

        # Iterate over active cores from Solr's STATUS response (cores are in
        # the status array of this response).
        for core in data["status"]:
            # Pattern to match, for example: statistics-2018
            pattern = re.compile("^statistics-[0-9]{4}$")

            if not pattern.match(core):
                continue

            # Append current core to list
            statistics_core_years.append(core)

    # Initialize a string to hold our shards (may end up being empty if the Solr
    # core has not been processed by stats-util).
    shards = str()

    if len(statistics_core_years) > 0:
        # Begin building a string of shards starting with the default one
        shards = f"{SOLR_SERVER}/statistics"

        for core in statistics_core_years:
            # Create a comma-separated list of shards to pass to our Solr query
            #
            # See: https://wiki.apache.org/solr/DistributedSearch
            shards += f",{SOLR_SERVER}/{core}"

    # Return the string of shards, which may actually be empty. Solr doesn't
    # seem to mind if the shards query parameter is empty and I haven't seen
    # any negative performance impact so this should be fine.
    return shards


def is_valid_date(date):
    import datetime

    try:
        # Solr date format is: 2020-01-01T00:00:00Z
        # See: https://docs.python.org/3/library/datetime.html#strftime-strptime-behavior
        datetime.datetime.strptime(date, "%Y-%m-%dT%H:%M:%SZ")

        return True
    except ValueError:
        raise falcon.HTTPBadRequest(
            title="Invalid parameter",
            description=f"Invalid date format: {date}. The value must be in format: 2020-01-01T00:00:00Z.",
        )


def validate_items_post_parameters(req, resp, resource, params):
    """Check the POSTed request parameters for the `/items` endpoint.

    Meant to be used as a `before` hook.
    """
    import json

    # Only attempt to read the POSTed request if its length is not 0 (or
    # rather, in the Python sense, if length is not a False-y value).
    if req.content_length:
        doc = json.load(req.bounded_stream)
    else:
        raise falcon.HTTPBadRequest(
            title="Invalid request", description=f"Request body is empty."
        )

    # Parse date parameters from request body (will raise an HTTPBadRequest
    # from is_valid_date() if any parameters are invalid)
    if "dateFrom" in doc and is_valid_date(doc["dateFrom"]):
        req.context.dateFrom = doc["dateFrom"]
    else:
        req.context.dateFrom = None

    if "dateTo" in doc and is_valid_date(doc["dateTo"]):
        req.context.dateTo = doc["dateTo"]
    else:
        req.context.dateTo = None

    # Parse the limit parameter from the POST request body
    if "limit" in doc:
        if isinstance(doc["limit"], int) and 0 < doc["limit"] < 100:
            req.context.limit = doc["limit"]
        else:
            raise falcon.HTTPBadRequest(
                title="Invalid parameter",
                description=f'The "limit" parameter is invalid. The value must be an integer between 0 and 100.',
            )
    else:
        req.context.limit = 100

    # Parse the page parameter from the POST request body
    if "page" in doc:
        if isinstance(doc["page"], int) and doc["page"] >= 0:
            req.context.page = doc["page"]
        else:
            raise falcon.HTTPBadRequest(
                title="Invalid parameter",
                description=f'The "page" parameter is invalid. The value must be at least 0.',
            )
    else:
        req.context.page = 0

    # Parse the list of items from the POST request body
    if "items" in doc:
        if isinstance(doc["items"], list) and len(doc["items"]) > 0:
            req.context.items = doc["items"]
        else:
            raise falcon.HTTPBadRequest(
                title="Invalid parameter",
                description=f'The "items" parameter is invalid. The value must be a comma-separated list of item UUIDs.',
            )
    else:
        req.context.items = list()